Guys I really want a AR, but I am completely ignorant of the AR platform. So what I need is a meat and potatoes rundown of components and options. Such as carbine length and mid-length and what part exactly are those lengths pertaining to. Gas system vs. Piston system pros cons and what it actually is...etc. details are appreciated. Any "need to know info" is what I need. Thanks so much

"...rough men stand ready in the night to visit violence on those who would do us harm." /G\

Well carbine, mid-length, and rifle length refers to the length of the gas system, or how far down the barrel the gas tube attatches to it via the gas block. The gas block can either be part of the front sight or a low profile gas block that usually hides under a free floating hand guard. A free floating hand guard means that it doesn't come into contact with the barrel foward of the barrel nut (essentally a large screw or nut that keeps the barrel attatched to the upper receiver). Free floating hand guards and good quality barrels contribute greatly to accuracy due to harmonics and temperature change of the barrel as you shoot, or even just the ambient air temp and humidity. If the barrel's not touching any other part of the rifle there's nothing to affect it's movement as the bullet travels down it (and it does move, check out high speed footage) and temperature extremes, like a really hot barrel and a cool handguard wont throw it off either. So that's something to keep in mind for sure, a good barrel such as a cold hammer forged or match grade bull barrel with crome lining along with a free floating forend will tighten up your groups a bit. As far as what length barrel to get... They range from 10" to 24", but anything shorter than 16" will require NFA (National Firearms Act) paper work. The three most popular are 14.5", 16" and 20" barrels. Which one to choose depends as much on what type of look you're going for as what the perfomance differences are and what you plan on using it for. It's really personal preference, although obviously more length means more velocity, accuracy, range, and stoping power. That briefly covers the boomstick part, onto the guts of an AR.
There's one part of the AR that's been essentially unchanged since 1965, the receiver. The M-16A1,A2,A4 , the M4, the AR-15- they all use the same basic receiver and shoot the same ammo. The only real difference between them is the length of the barrel and it's gas system and the size of the buffer, or recoil, system they have. The receiver is made out of a solid block of aluminum, a CNC machine drills out the useless metal and forms the parts. So the receiver is actually really strong, stronger than a stamped metal AK, yet lightweight. The receiver consists of two main parts- the upper receiver and the lower receiver. The upper has the barrel attatched at the front, the bolt carrier group in the middle, and the buffer tube and spring at the back (the buttstock). There are some options when it comes to the upper receiver- you can get a standard A2 style upper, which is one that has the M-16 style carrying handle and rear sight perminantly attatched. Or you can get a flat top upper, which has a modular rail system incorperated into the top of it. A flat top is much more versatile as you can easily attatch any kind of steel sight, red dot, or magnified optic you like. The other main option for your upper receiver is whether or not it's crome lined. A crome lined upper and bolt carrier will wear a lot slower and clean up a bit easier. The lower is where the magazine well, bolt catch, trigger assembly, selector switch, pistol grip, and buffer system (buttstock) are. There are oodles of after market parts for AR's, not the least of which are trigger groups, pistol grips, and buttstocks. All three of those options are again personal preference and I'd recomend sticking with the stock components at first. Once you get a feel for the rifle you'll know what kind of trigger, buttstock and grip you want, and they're easy enough to change yourself. The only other real option as far as the lower's concerned is the buffer tube. There are carbine and rifle buffer tubes which use either carbine or rifle buffers and springs respectively. That's the part of the rifle that forces the bolt back fowards and loads another round. It also absorbs some of the recoil, a rifle length buffer tube and spring will absorb slightly more recoil than a carbine buffer. But don't get overly concerned about the recoil because with 5.56x45mm NATO or .223" Rem it's pretty laughable no matter what you're shooting it out of. Most new AR's come with carbine length buffers to accomidate the popular adjustable buttstocks, but keep in mind that the kind of buffer doesn't neccessarily have anything to do with the length of barrel or length of gas system, i.e. carbine, mid-length, or rifle. They're all compatible with either a rifle or carbine buffer.
As far as the operating sytem's concerned; the good old gas impingment sytem's been working just fine for 45 + years now. You can go with the gas piston system, it does keep the bolt cooler and the receiver cleaner, but it's also heavier and more complicated, more to go wrong. All and all the AR's almost infinately customizable, Lego's for big boys, so figure out what style you like, what look you're going for and what you'll be using it for and go for it. You can always change stuff afterwards. Hope that helps.

Guys I really want a AR, but I am completely ignorant of the AR platform. So what I need is a meat and potatoes rundown of components and options. Such as carbine length and mid-length and what part exactly are those lengths pertaining to. Gas system vs. Piston system pros cons and what it actually is...etc. details are appreciated. Any "need to know info" is what I need. Thanks so much

"...rough men stand ready in the night to visit violence on those who would do us harm." /G\

my suggestion is this, buy a complete basic model first, shoot it, practice with it, learn how it works, learn how to strip it down to clean it and maintain it. learn what you would want differently on it, then build the one you want. good starter AR's, Bushmaster, Rock River Arms, Del-Ton and many others. if you shop around, you can probably get a basic and decent one for less than $900 or so. check out your gunstores and pawn shops as you might find a good deal on a decent used one. this is the route i took with my first one, my next one will be built from the ground up into what makes me happy.

Sorry, correction; I said the upper receiver has the buffer tube attatched to it at the back... It doesn't, that's the lower receiver. What I was trying to get at is the in line set up of all the major operating parts. The barrel, bolt and operating spring are all in a straight line, which is pretty unique and is a big part of the reason the AR has been so successful. That's what enables it to be so accurate and be virtually recoilless.

Here are some basic, general diagrams of the AR platform, I also threw in a bullet comparison chart, hope it helps.
I bought my LAR-8 (308/7.62x51) used but un-fired. Now I'm selling the parts that I'm changing out, to personalize it a bit. That's HALF THE FUN..!

So why do they make different lengths? Carbine mid and such? What are advantages of each?

"...rough men stand ready in the night to visit violence on those who would do us harm." /G\

Now I believe each group (carbine, mid, etc.) had a different specific job. the lighter shorter weapons were equipped with different accessories so they would be easier to carry for troops that carried them walking, or for paratroopers, or pilots that need to carry a rifle, and so on.

The AR platform was originally, SOLELY, a combat platform. Each group had a designated military purpose.

Isn't that correct guys..? Or close..?

__________________The EARLY bird may get the worm... But the SECOND mouse gets the cheese..!!!

______
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
________________________________________
US Army 1966-69, VFW Life Member, Retired Geek